Fitting arrangements for effecting a compressive sealed engagement to the end of a nonthreaded tube, particularly a plastic tube, are well known. Such fitting arrangements conventionally employ a fitting body which has a collar part which telescopes onto the end of the plastic tube, which collar part is threadably engaged with an annular nut which surrounds the tube. The annular nut and collar part have opposed interior conical seats, and a ferrule and a gripper ring are disposed in surrounding relationship to the tube between the opposed conical seats on the nut and collar part. These rings have exterior conical surfaces which cooperate with the seats, with the gripper ring also having interior teeth adapted to bite into the plastic tube. Threading of the nut onto the collar part causes axial compression of the rings between the opposed seats, and radial compression of these rings into sealing engagement with the plastic tube. Fitting arrangements of this type are extensively utilized in conjunction with plastic tubes which are used for confining and transporting dangerous fluids, for example high temperature and/or caustic fluids (such as acids), such as extensively utilized in the semiconductor industry.
Copending application Ser. No. 092 163, owned by the assignee of this application, illustrates therein an improvement with respect to a fitting arrangement of this general type. The disclosure of this copending application is incorporated herein, in its entirety, by reference.
Fitting arrangements of the above-mentioned types are suitable for sealingly engaging only a single plastic tube. However, in some instances it is desirable to utilize concentric inner and outer plastic tubes, with the outer tube hence functioning as a containment for loosely surrounding the inner tube through which the main fluid flows. For example, when using this outer concentric tube so that there is additionally defined an annular passage within the outer tube in surrounding relationship to the inner tube, this additional passage can have a sensor fluid supplied therethrough so as to detect any leaks from the inner tube. Another possible usage for the outer tube is the ability to pump a heated liquid therethrough in surrounding relationship to the inner tube for maintaining temperature control of the primary or inner tube. A further possibility is merely the ability to pump a second liquid coaxially by means of this additional passage. A still further possible use for this outer tube is due to the fact that the tubing is conventionally Teflon and hence exhibits an effusion problem with respect to some gases such as natural gas, nitrogen and the like, so that small quantities effuse through the wall of the tube and these small quantities will hence be trapped in the outer passage defined by the outer tube. This outer passage can have a shielding gas pumped therethrough for monitoring such leakage. Further, this outer tubing basically provides a second wall for safety purposes, as when pumping liquids such as hot acids.
At the present time, in situations where concentric inner and outer plastic tubes are being used, the inner tube has the end thereof compressingly sealed to a standard fitting of the type described above. The adjacent end of the outer tube must also be sealed at substantially the same location, and such applications currently use a standard hose clamp for sealingly clamping the end of the outer tube to the inner tube. Use of a conventional hose clamp in this type environment, however, is less than desirable since in many instances this clamping occurs directly between the tubes and hence the outer tube does not provide a second seal effective for confining any leakage through the fitting arrangement. Further, hose clamps themselves are highly questionable as to the seal which is achieved between the tubes.
Accordingly, this invention relates to an improved fitting arrangement for use in sealing engagement with concentric inner and outer plastic tubes, which fitting arrangement creates a double shield or seal in that it sealingly engages the ends of both the inner and outer tubes thereby providing an arrangement which is more effective in performance and efficient to utilize then the prior known structures.
More specifically, in the improved fitting arrangement of the present invention, the same is provided with three main body parts, namely a fitting body which telescopes onto the end of the inner tube, a nut which surrounds the adjacent end of the outer tube, and an intermediate annular body which is disposed in surrounding relationship to the tubes axially between the nut and fitting body. This intermediate body has a collar part at one end which cooperates with the nut, and a nut part at the other end which cooperates with the fitting body. The nut part and fitting body compress ferrule and gripper rings therebetween into sealing engagement with the inner tube, and similarly the collar part and nut compress therebetween a further pair of ferrule and gripper rings into sealing engagement with the outer tube. Two highly effective compressive seals are thus obtained.
Other objects and purposes of the invention will be apparent to persons familiar with fitting arrangements of this general type upon reading the following specification and inspecting the accompanying drawings.